Oil sealing of rotary piston vacuum pump



July 29, 1969 PFAFF ET AL 3,458,120

OIL SEALING OF ROTARY PISTON VACUUM PUMP Filed 001. 6, 1967 2 Sheets-Sheet 1 I 21. Flg2 g 224 Fig.1

f/ANSE/V PFAFF HART/W07 SIN/V MAX/MM /A/v WUTZ Inventors July 29, 1969 H. PFAFF ET AL 3,458,120

OIL SEALING OF ROTARY PISTON VACUUM PUMP Filed Oct. 6, 1967 2 Sheets-Sheet 2 Fig.4

United States Patent Int. (:1. F04c 17/02, 27/00 US. Cl. 230-145 3 Claims ABSTRACT OF THE DISCLOSURE An eccentrically operating hypotrochoidal form piston is continuously engaged against a contact line of the housing contiguous with a pressure port which is enlarged adjacent the line of contact to permit oil to escape into the pressure spot. A sealing strip may additionally be provided at the line of contact which is recessed to conform to the enlargement in the pressure port.

The present invention concerns an oil sealed rotary piston vacuum pump having a piston of hypotrochoidal form rotating eccentrically within a housing forming a corresponding outer cover. :In such a pump the piston contacts at least one point of the housing during its rotation.

Rotary piston machines may be used as pumps, but from the very many usable forms of machine, only specific ones can be used to obtain a very high or medium degree of vacuum -10 torr). It has been found that machines having hypotrochoidal form rotary pistons and a tranmission ratio of 1:2 or 2:3 are useful. In these machines the space to be evacuated starts with zero volume and dead spaces do not occur. The runner or piston has two or three corners. In such machines, there is at one or two points, in a fixed part of the pump which forms a mantle, a predetermined location forming a point or corner. These points separate the suction and the pressure side and the rotary bodies fit against them in any phase of motion.

In use as a vacuum pump, it is of advantage that the parts which separate the pressure and the suction sides are sealed off by oil. A high degree of sealing is necessary in vacuum pumps, and it can happen that during the compression phase the sealing oil is moved by the piston along its contact line with the housing and reaches the suction side. If the oil film is not continuous over the axial line of contact of the piston with the housing, then leakages result; furthermore, a disadvantage occurs in that oil gains the suction side due to the high speed which it attains as it is pressed past the contact line. Since the sealing oil contains entrained gas, the gas could escape therefrom at the suction side.

In order to overcome the above-mentioned disadvantages, it is proposed, in accordance with the present invention, to form the pressure port so that it is contiguous with a contact line, formed in the housing of the vacuum pump, for continuous engagement by the piston as it rotates. To assist in the escape of oil to the pressure side, the pressure port may be slightly enlarged. Advantageously, a radially resilient sealing strip is provided at the contact line and this may be suitably recessed to correspond in shape to the enlargement of the pressure port.

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The structure, organization and operation of the invention will now be described more specifically with reference to the accompanying drawings, wherein:

FIG. 1 is a cross-section through one embodiment of pump housing and hypotrochoidal form piston constructed in accordance with the invention;

FIG. 2 is a similar cross-section in which the piston is in a different position;

FIG. 3 is a similar cross-section but of a second embodiment of the invention; and

FIG. 4 is a cross-section of the embodiment shown in FIG. 3 in which the piston is in a different position.

In the drawings like reference numerals denote like parts.

In both examples of the machine the transmission ratio is 1:2.

A piston 12 rotates in a pump housing 10 in the direction of the arrow, the drive for the piston being by means of an eccentric drive (not shown). The piston 12 rolls on an inner gearing 16 meshing with a pinion 14 fixed to the housing 10. During its rotation, the piston 12 runs against a point 18 of the housing 10 which point is located between a suction port 20 and a pressure port 22. When the pump is employed as a vacuum pump, it is usually used with oil for sealing. 'If the piston 12 reaches the FIGURE 2. position, then almost maximum pressure differential is reached. If the piston 12 moves slightly further, the pressure port 22 is practically closed 01f by the piston 12. The sealing oil which is carried along is pushed ahead by the piston 12 as a small oil lake and collects in front of the point 18 and could in the ordinary construction, as the piston rotates, not escape into the pressure port 22. At high pressure differential the oil could be pushed beyond the edge 18 and, in view of the high oil speed, be pushed into the suction port 20* where it could de-gas itself. This, however, is avoided by forming a small rabbet 24 in the pressure port 22 near the point 18. The sealing oil can now enter into the thus enlarged port 22 through the rabbet 24 and can escape therefrom even under maximum pressure dilferential.

In the embodiment shown in FIGURES 3 and 4 a groove or recess 26 is formed at the point 18 in the housing 10. A sealing strip 28 is placed into the recess 26 and is radially resiliently held there. During the running of the piston, the strip 28 compensates for tolerances in manufacture and for vibrations of the piston during operation. The sealing strip 28 is provided with an increased chamber 30 which connects with the pressure port 22. The increased chamber 30 can be made easily by milling out a portion of the sealing strip 28. The pressure port 22 is thus extended to the region of the point 18, and perfect operation with good efliciency is obtained.

Further features of a pump in accordance with the present invention are shown and described in detail in the co-pending applications by the inventor herein filed at the same date Oct. 6, 1967 and entitled:

Transmission Drive for Rotary Piston Vacuum Pump, Ser. No. 673,427; End Face Sealing in Rotary Piston Vacuum Pump, Ser. No. 673,337; Oil Circulation in R0- tary Piston Vacuum Pump, Ser. No. 673,336.

We claim:

1. An oil sealed rotary piston vacuum pump having a housing, an eccentrically rotatable hypotrochoidal piston located in the housing, said housing having the form of the appropriate enveloping figure therefor, and having a contact line continuously engaged by said piston as it rotates, a pressure port being formed in said housing, said 3,458,120 3 4 pressure port extending Within said pump housing up to References Cited said contact line of the enveloping figure. UNITED STATES PATENTS 2. Pump accordlng to claim 1 includmg a recess in the pressure port formed adjacent said contact line. 3,289,646 12/1966 Paras- 3. Pump according to claim 1 including a radially re- 5 3,303,830 2/1967 Fingeroot et a1 230 145 silient sealing member located at said contact line, said WILLIAM L FREEH P i E iner sealing member being formed with a recess communicating with the pressure port WILBUR J. GOODLIN, Assistant Examlner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,458,120 July 29, 1969 Hansen Pfaff et a1 It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, lines 6 and 7, "5 Co. KG, Cologne-Bayental, Germany, a firm of Germany" should read Koln-Bayental Germany Signed and sealed this 21st day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

